From an evolutionary perspective, altruistic behaviour is still a bit of mystery to psychologists, especially when it comes with a hefty cost to the self and is aimed at complete strangers.

One explanation is that altruism is driven by empathy – experiencing other people’s distress the same way as, or similar to, how we experience our own. However, others have criticized this account – most notably psychologist Paul Bloom, author of Against Empathy: The Case for Rational Compassion. Their reasons are many, but among them is the fact that our empathy tends to be greatest for people who are most similar to us, which would argue against empathy driving the kind of altruism that involves the giver making personal sacrifices for strangers.

Hindering research into this topic is the challenge of measuring empathy objectively and devising a reliable laboratory measure of altruism (including one that overcomes most volunteers’ natural inclination to want to present themselves as morally good).

A new study in Psychological Science overcomes these obstacles by using a neural measure of empathy and by testing a rare group of people whose altruistic credentials are second to none: individuals who have donated one of their kidneys to a complete stranger.

The findings suggest that – at least for this group of “extraordinary altruists” – empathy for others may be a relevant driving force. Compared with demographically matched controls, the altruists showed a greater amount of overlap in the neural activity they exhibited during their first-hand experience of pain and when observing a stranger in pain.

The US research team, led by Kristen Brethel-Haurwitz at the University of Pennsylvania, invited the 25 kidney donors and the 27 controls to their lab and had them complete various sessions in the brain scanner, during which they either experienced painful pressure applied to their own thumb, or they witnessed a live video feed of a previously unfamiliar study partner (actually a research confederate) suffering the same pain. For comparison, some sessions for both the participant and their partner were completely safe and pain-free, allowing the researchers to investigate brain activity during experienced pain, the anticipation of possible pain, and during safety.

At a group level, the altruists exhibited greater neural overlap while experiencing pain and while witnessing a stranger in pain, including in the left anterior insular, putamen, thalamus, prefrontal cortex and cingulate cortex (all known areas of the brain’s “pain matrix”). The altruists also showed greater neural overlap when anticipating pain themselves and when anticipating that their partner would experience it. These group contrasts are despite the altruists and controls showing comparable average patterns of neural activation when experiencing pain, or the threat of it, themselves.

At an individual level, for the altruists but not the controls, the neural activation they showed in the left anterior insular while in pain correlated with the amount of activation they showed in that same region when observing their partner in pain.

Moreover, the researchers also looked at neural connectivity patterns, finding that the altruists displayed greater functional connectivity between pain-related neural regions during first-hand pain and when observing another in pain, as compared with the controls.

The psychological relevance of the neural findings were supported by the fact the altruists expressed a greater sense of inclusion of their partner in their sense of self (than did the controls), and this sense of closeness appeared to mediate at least some of the neural overlap they exhibited between first-hand and empathic pain.

In contrast to the neural data, the “inclusion in self” scores, and the super-altruists’ history of organ donation, the controls rated themselves just as empathic as did the super altruistic kidney donors, which surely places a question mark over the validity of much of the existing literature in this field that has relied on such self-rating measures.

The researchers acknowledged that their findings may not generalise to less exceptionally altruistic people. However, they believe their work demonstrates an important point that will inform the debate about the role of empathy in altruism. “That altruists, relative to controls, exhibit enhanced self-other mapping for strangers’ distress – ordinarily observed only in response to close others – supports the hypothesis that empathic biases against distant or dissimilar others can be overcome,” they said, “and that, ultimately, empathy can support the provision of costly altruism.”

And you don’t think your generalization of kidney donors is irrational? Correct me if I’m wrong, but kidney donors are a decent size group of people scattered throughout the world. How many of these people have you actually met? What data sets have you collected to come to your mind boggling, limited conclusion that takes an entire subset of human beings and clones them and files them under “extremely low self esteem, irrational or delusional beliefs and so on”? What exactly are the “so-on’s”? What knowledge and experience do you yourself have regarding empathy and altruism? What measures, if any, have you found you yourself possess of these character traits?

On anonymous donation of a kidney, we have to wonder at the psychological makeup of such an individual. Do they donate in other ways, have they been convinced by some logical argument to donate in just this way, do they believe there is some kind of ethereal reward such as heaven or a favourable rebirth and so on.